If you’re having difficulty getting iStat for iPhone to connect to iStat Server, there’s a chance the connection is being blocked by a firewall.
If you’re using the in-built firewall in Mac OS X 10.4 Tiger: go to System Preferences > Security > Firewall and allow the port you’ve set in iStat Server.
If you’re using the in-built firewall in Mac OS X 10.5 Leopard: go to System Preferences > Security > Firewall and allow /Library/Application Support/iStat Server/iStatServer.
Please refer to the specific help documentation that came with your hardware or software.